Ear plugs



EAR PLUGS Filed Aug. 31, 1959 INVENTOR. JOZEF J. ZWISLOCKI.

ATTORNEY.

United States Patent This invention relates to earplugs, and moreparticularly to earplugs capable of substantially uniform soundattenuation through a substantial range of audible frequencies.

The development of increasingly powerful engines has ledto noise levelsthat interfere with auditory communication, and, sometimes, are harmfulto the human organism. Conventional earplugs producing an average.

sound attenuation of 20 to 30 decibels are insuflicient for a growingnumber of industrial and military situations. They have been graduallyreplaced by ear muffs that enclose the whole ear and, when suffioientlylarge, provide to 20 decibels more attenuation than earplugs at mediumand high frequencies. For communication purposes, earphones are securedunder the ear muffs.

The ear muffs for ear protection against ambient noises have two basicdisadvantages. In the first instance, they are bulky and cumbersome, andmay interfere with additional equipment worn on the head, as for examplecrash helmets. In the second instance, the large volume of air enclosedbetween the shell of an effective ear muff and the ear drumsubstantially decreases the efiiciency of the earphone mounted in theear muff.

Due to the disadvantages of ear muffs, numerous attempts have been madeto increase the sound attenuation provided by earplugs. It has beenfound that this attenuation is inversely proportional to the acousticimpedance produced at the tip of the earplug by the ear drum and thevolume of air enclosed in the ear canal; the larger the volume, thelower the resultant impedance and the higher the attenuation. The volumeenclosed between the earplug and the car drum is determined by theanatomy of the ear canal. Nevertheless, the effective volume can beincreased by coupling an external'enclosure through a perforation in theearplug. Experirnental devices of this kind, that became known in thepast, produced the desired effect at low frequencies. However, atfrequencies around 1,000 cycles per second, or above, the soundattenuation was decreased as compared With solid earplugs.

It is, therefore, the principal object of the present invention toprovide earplugs of novel construction, with an enclosed volume of airconnected to the external ear canal in such a way that the soundattenuation at frequencies below 1,000 cycles per second is increasedabove the level obtained without the additional volume, and atfrequencies between 1,000 and 6,000 cycles per second either increasedor practically unchanged. Higher frequencies are of little importance tocommunication and ear protection. I

It has been determined theoretically and confirmed expermientally thatan enclosure coupled to the ear'canal by means of a tube can increasethe sound attenuation produced by an earplug at low frequencies Withoutdecreasing it at higher frequencies, provided the tube is sufficientlywide and short. The enclosure with the connecting tube constitutes anacoustic resonator with a negative input reactance at low frequenciesand a positive one above the resonance frequency. The input reactance atthe entrance to the ear canal is negative up to about 2,500 cycles persecond and becomes positive at higher frequencies. When the resonatorreactance changes its sign at a frequency lower than 2,500 cycles persecond, an anti-resonance may be produced, leading to a deice creasedsound attenuation. In order to prevent this condition, the inertance ofthe resonator, which is determined by the dimensions of the couplingtube, must remain small. It has been found, for instance, that acoupling inertance of 4 l0 g./om. does not decrease attenuation with anyresonator volume. When the inertance is increased to 10 g./cm. themaximum decremen-t of attenuation below the reference level amounts toabout 5 decibels with a resonator volume of 6 cubic centimeters and 4decibels with a resonator volume of 4 cubic centimeters. The attenuationdrop of 5 decibels should be considered a tolerance limit.

More specifically, it is an object of the invention to provide earplugscontaining an essentially rigid enclosure ending on one side in atubular member, said tubular member designed to connect the air volumeof the enclosure to the ear canal and having an acoustic inertance ofless than 10' g./cm. Such a small inertance which requires a short andwide tube can only be obtained when the enclosure is of a shape fillingapproximately the inner portion of the outer ear. An example of such ashape is .given in the accompanying drawing.

It is another object of the invention to provide ear plugs containing anenclosure ending in a tubular member, as specified above, so designedthat they can be comfortably secured in the car without external supporting means.

It is another object of the invention to provide earplugs containing anenclosure, open toward the ear canal, and shaped and constructed in sucha way that they can be comfortably secured in the car without externalsupporting means.

It is a further object of'the invention to provide earplugs containingan enclosure, as specified above, shaped and constructed in such a waythat they can be held against the entrance to the ear canal by means ofa headband, thereby providing a hermetic coupling between the enclosureand the ear canal.

It is a further object of the invention to provide at the outer wall ofthe enclosure means for hermetic attachment of an ear phone forcommunication purposes.

The above and other objects of the invention will appear more fullyhereinafter from the following detailed description when taken with theaccompanying drawings. It is expressly understood that the drawings areemployed for purposes of illustration only and are not designed as adefinition of the limits of the invention, reference being bad for thispurpose to the appended claims.

In the drawings, wherein like reference characters indicate like parts:

FIGURE 1 is a view in side elevation of a preferred form of earplugembodying the invention;

FIGURE 2 is a view of said plug from the top of FIGURE 1;

FIGURE 3 is a view of said plug from the bottom of FIGURE 1;

FIGURE 4 is a sectional elevation taken on line 44 of FIGURE, 2; 7

FIGURE 5 is a side elevation of a modified form of earplug embodying theinvention with a portion in section; and i FIGURE 6 is a view insideelevation of an earplug having a small car phone attached thereto.

The earplug according to the preferred embodiment shown in FIGURES l-4comprises an enclosure 10 open toward the ear canal through a tubeportion 12, and a sealing tube 14.

The walls 16, 18 of the enclosure, including the top cover 20, and thetube portion 12, are made of a rigid material of sufficient thickness toproduce the necessary sound attenuation. The Wall thickness depends onthe rigidity of the material.

When metal alloys, fiberglass,

The sealing tube 14 is made of a soft resilient material,

as for example, polyvinyl chloride or silicone rubber. It is removablysecured on the tube portion 12 by means of a groove 22 and flange 24 inthe ear plug tube por tion, and sealing tube respectively.

The sealing tube is divided into four sections: the opening area 26, theconvex portion 28, the neck portion 30 and the flange 24. At the levelof the flange, there is a finger tab 34 which serves to remove thesealing tube from the ear canal, should it .become'detached and remainthere by accident, after the rest of the earplug has been removed. Thecross section of the sealing tube is essentially round or slightlyelliptical, and the convex portion 28 is made in several sizes in orderto better conform to variations in the size and shape of the individualsear canals to which it is to be adapted. The pear-like shape of tube 12helps to retain the earplug in the ear canal, and provides a tight sealagainst the outside air. At the same time the sealing tube allows theacoustic inertance, coupling the earplug'enclosure to the ear canal, toremain at its practical minimum. By

. acoustic inertance is meant the product of the efiective length of thetube and the density of the medium, divided by the effective crosssectional area of the tube.

The rigid enclosure is shaped to conform approximately to the conchaportion of the outer ear of the majority of people. It is widest in thevicinity of the cover and narrowest in the tube portion 12 which isinserted into the ear canal. The cross-section in the vicinity of thecover 20 is circular and becomes gradually elliptical in the midportionof the enclosure, with the long axis in the plane of FIGURE 4. In thevicinity of the groove 22 the crossection is circular again and becomeselliptical in the tube portion 12, with the long axis perpendicular tothe section plane of the FIGURE 4. The wall portion 18 has a slightreverse curve and fits approximately the contour of the anti-tragus ofthe outer car. This shape helps effectively in retaining the earplug inthe ear.

The volume of the' earplug enclosure amounts to approximately 2 cubiccentimeters. The tube portion is approximately 0.8 centimeter long andits crossection area is an average .24 square centimeter.

When well fitted, the earplugs produce a sound attenuation of somewhatmore than 40 decibels in the frequency range between 100 and 6000 c.p.s.

It is possible to modify the cover .20 so that a small earphone 21 canbe attached to it. The alternative design is shown in FIGURE 6. In thisdesign, cover 20 replaces cover 20 of FIGURE 4. Cover 20' comprises acentral opening which provides a passage for the sound from the earphoneand at the same times serves as a means. for attaching said earphone.

An alternative construction embodying the general principle of theinvention is illustrated in FIGURE 5. In this embodiment the enclosureportion 50 which is essentially the same as the enclosure 10 in FIGURES1-4 is extended by an additional enclosure 52. The two parts of theenclosure communicate with each other through a Wide opening. Theenclosure portion 52 is closed by a cover 54, carrying a headband holder56 for the attachment of a headband not shown.

The tube portion 58 is short. It has an internal groove 60 for theattachment of a sealing ring 62. The sealing ring is adapted to lit theentrance to the ear canal of the majority of people. It carries a flange64 for attachment to the tube 58 and a safety tab 66 which performs thesame function as the tab 34. The cross section of both. the tube 58 andthe sealing ring 62 are oval or elliptical with the long axisperpendicular to the plane of FIGURE 5.

The walls of the enclosure 50 and 52 and of the tubular portion 58 aremade of a rigid material; the sealing ring 62, of a soft resilientmaterial.

While the invention has been described and illustrated as embodied incertain specific examples of earplugs carrying the internal enclosure,it is to be understood that the invention is not so limited andcomprehends other forms and configurations within the terms of theclaims.

What is claimed is:

1. An ear plug comprising an essentially rigid thin wall enclosurehaving a volume in the order of 2 cubic centimeters, said enclosureending at one side in a short thin wall rigid tubular portion adaptedfor communication with the ear canal and of a length in the order of 0.8centimeter, said tubular portion having an acoustic inertance of lessthan 10* g./cm.*.

2. An ear plug according to claim 1, wherein the enclosure ispearshape-d so as to nest in the concha region of the ear withoutprotruding substantially beyond the auricle.

3. An ear plug according to claim 1, wherein the tubular portion isprovided with means tforhermetically sealing the end thereof to the wallof the ear canal.

4. An ear plug according to claim 8, wherein the tubular portion isprovided with a soft resilient coupling member adapted to seal the endof the tubular portion to the ear canal, and secure the plug inposition.

5. An ear plug according to claim 1, wherein the enclosure is providedwith an outer wall, and the wall is provided with a connection for ahead band for sealing under slight pressure.

6. An ear plug according to claim 1 wherein the enclosure is providedwith a cover plate and an earphone mounted thereon.

References Cited in the file of this patent Norway o Oct. 14,

